Lubricants comprise a variety of additives in a base mixture selected for desirable characteristics such as anti-wear and anti-friction properties. Often commercial lubricants are compositions containing a lubricant base such as a hydrocarbon base oil or base grease (oil to which a thickener has been added to form a solid), to which are added numerous lubricant additives selected for additional desirable properties. Lubricant additives may enhance the lubricity of the lubricant base and/or may provide anti-wear or other desirable characteristics.
Lubricants are used in enormous quantities. For example, more than four billion quarts of crankcase oil are used in the United States per year. However, many lubricants currently in use also have undesirable characteristics. Currently available crankcase oils generally include the anti-wear additive zinc dialkyldithiophosphate (ZDDP), which contains phosphorous and sulfur. Phosphorous and sulfur poison catalytic converters causing increased automotive emissions. It is expected that the automotive industry will eventually mandate the total elimination of phosphorous and/or sulfur, or will allow only extremely low levels of phosphorous and/or sulfur in crankcase oil. However, no acceptable anti-wear additives to replace ZDDP in engine oils are currently available. Greases require both anti-wear and extreme pressure (EP) characteristics. These characteristics are measured in 4-ball testing machines. Anti-wear behavior is measured by the size of the wear scar in 4-ball wear tests, while EP is measured by weld load and Load Wear Index (LWI) in the 4-ball weld tests. It is extremely difficult to simultaneously achieve both good anti-wear and good EP characteristics in a single grease.
Additionally, lubricant bases used in conventional lubricants usually have lubricant additives added to them to improve lubricity and other performance characteristics. Many of these lubricant additives do not provide sufficient additional lubricity or other performance characteristics, and/or possess additional undesirable characteristics.
Accordingly, it is an object of the present invention to provide environmentally-friendly anti-wear additives for lubricants, wherein the amounts of phosphorous and sulfur which are contributed by the anti-wear additive to the lubricant are significantly reduced and approach zero. It is another object of the present invention to produce additives with desirable anti-wear and anti-friction characteristics. It is another object of the present invention to provide improved anti-wear and EP characteristics in greases.